To enhance passenger comfort, elevator systems require acceleration control systems to suppress accelerations, e.g., vibrations, transmitted from various components of the elevator system to the elevator car. Most elevator systems provide one or more means for absorbing or dampening forces applied to an elevator car by surrounding structures. For example, friction dampers may be applied to roller guides. Such solutions add to the cost and space requirements of the overall system, and are subject to high levels of wear. Active-guidance control systems have been employed to reduce or eliminate certain types of vibrations associated with elevator car movement.
One factor that greatly affects elevator car ride quality is lateral vibration of the elevator car with respect to the hoistway or elevator guide rails. Lateral vibrations can be caused by aerodynamic forces acting directly on the elevator car during movement. Lateral vibrations may also be attributable to suspension forces resulting from imperfections in the manufacture and installation of the hoistway guide rails, or due to misalignment of the rails caused by building settlement.
Certain known systems stabilize the elevator car frame with respect to the hoistway guide rails. Systems of this type require a suspension-centering subsystem that adds weight, cost, and complexity to the overall elevator system. These types of systems are often subject to reliability problems. In addition, they typically consume large amounts of electrical power which requires additional cost and which presents thermal concerns. By stabilizing only the elevator car frame with respect to the hoistway guide rails, there still remains relative movement or vibration between the elevator car frame and the cab floor, on which the passengers stand.
At least one known system described in a publication, "Improving Control of Super-High-Speed Elevators", Japan Society of Mechanical Engineers International Journal, Series C, Vol. 40, No. 1 1997 (the JSME Article), attempts to control lateral vibration in an elevator car by using an actuator attached between the elevator car frame and the elevator cabin. The intent is to isolate the elevator cabin from vibrations to which the elevator car frame is subject. The results are somewhat mediocre, however, as described in FIGS. 18 and 19 of the JSME Article, because the ballscrew actuator used in the system introduces high frequency vibrations. In addition, the ballscrews will undergo mechanical wear, limiting life, increasing noise and decreasing maintainability. Moreover, the prior art system described in the JSME Article is subject to controllability problems due to stiction, friction and backlash of its mechanically contacting components.